Thermal switch



June 9, 1953 M. J. LAROCCO 2,641,668

THERMAL SWITCH Filed Aug. 3, 1949 DC INVENTOR 6 yz'cfiael 1020660 0 c J .Q z M 5? Patented June 9, 1953 THERMAL SWITCH 'Michael .I. Larocco, Berkeley, CaJi fb, ass'ignor to Motorola, -Inc., Chicago, 111., a -eorp'dration of Illinois Application August 3, 1949-, SerialNo. 108,283

9'Claims. 1

This invention relates to heater control systems, and particularly to thermal 'switches'for use in such systems.

In many heaters, particularly those of the combustion type, it is desirable that one or more thermal control switches be located close 'to'a heat source so that they may respond very quickly to the presence or absence of heat at said source for automatically controlling the operation of the heater. Such switches must withstand intense heat over long periods of time without deteriorating, and in many instances they are required to be extremely compact because of thelimited space available for mounting them. Where several heat-responsive switches serving different functions are required in the same control system, it is desirable-that these switches have as many identical parts'as possible for the most economical manufacture thereof.

An object of the present invention is to'provide an improved thermal switch of economical design which satisfactorily meets all of the requirements mentioned above.

Another object is to provide a novel heat-responsive control switch having an insulating base of simple and rugged construction to which an aibitrarily arranged stack of spring contact members may be secured by simple fastening means.

Still another object is to provide an improved heater control switch that can be produced with simple manufacturing facilities.

A feature of the invention is the provision of a thermal switch having a ceramic base with flatparallel leg portions andla flat transverse portion extending between said leg portions, together with a stack of aligned leaf members having portions thereof disposed between the legs of the base andsecured to the transverse portion thereof.

vAnother feature is the 'provision of novel fastening means for securing thestack'tothe switch base, such fastening means comprising a heatconducting rod having a threaded portion which extends through the switch stack and the transverse part of the base. A bimetallic contactactuating member in the stackis in heat-conducting relationship to the rod for actuating-the contact members in the stack as the temperature of the rod varies.

Still another feature is thep'rovision of a thermal switch that can be mounted in a very limited space closely adjacent to a heater, such switch comri'rising'a heat-conducting rod which serves both"to'mountthe-switch on the heater casing and toconductheat from a burner within'the casing'to the bimetallic actuating member of the switch, and an H-shaped ceramic base adapted to be secured to said rod and supporting a stack of aligned leaf members, one of which is "a bimetallic 'actuatingmember and'the others being contact members operated thereby. This assembly has the advantage that the leaf members can be arranged on the 'base to suit the convenience of the user.

The foregoing and other objects and features of the invention will be better understood from astudy of the following description thereof taken in connection with the accompanyin drawings, wherein: V

"Fig. l is a fragmentary, front elevational view of -a'heater assembly in which the present invention maybe utilized;

Fig. "2 is a vertical sectional view on the line 2- 2in Fig. :1; showing a thermal switch embodying the invention mounted in association with theheater; g Fig. 3 isa sectionalview of the switch taken on the'line--3 3 in Fig.2;

Fig. '4 is an' end elevational view of the switch;

Fig. '5 is a perspective view of the switch base;

Fig. 6 is a fragmentary sectional view of the heat conductingrod, taken on the line 66 in Fig. 4; and

Fig. 'i is aschematic diagram showing the manner in which the switch is associated with other parts of the heater control system.

In 'practicingth'e invention, the switch base is made of ceramic material and has an approximately H-shaped configuration. Leaf members consisting of resilient contact members and a bimetallic actuating member are stacked between. the legs of the H on both sides of the transverse portion thereof. A heat-conducting rod having 'a threaded end portion extends through the stack'and the transverse part of the base inheat conducting relation to the bimetalli'c actuating memberof the switch. This rod is provided with "a mounting nut that cooperates with "a nipple 'on' the heater casing for securing theswit'ch to this casing, with the rod extendinginto the flame zone of a burner within the casing. It also has a shoulder engageable with one side or the stack, anda nut is threaded on the 'irod-on the other side of the stack for securing the stack'to the transverse part of the switch' base, with thelegsiof the base preventing the leaf membersdromturning with respect to the rod.

The heater chosen for illustration in Figs. 1 and 2 is a small household type of heater which may be similar to that disclosed and claimed in copending application Serial No. 52,169, filed October 1, 1948, in the name of Stanley J. Budlane, entitled Heater and assigned to the present assignee, and which is adapted to burn vaporized liquid fuel such as kerosene, although the principles of the invention may be applied to other heaters as well. The burner section of the heater is enclosed within a casing l0, and adjoining this casing H] is a heat exchanger comprising finned ducts I2 through which combustion products pass to the exhaust duct (not shown) of the heater. Directly beneath the burner casing it is a compartment M in which a fan motor is housed. 7

Certain thermal control switches are associated with the heater to govern the operation thereof. Some of these switches are responsive to the presence or absence of combustion within the burner casing It. A switch of this character, indicated generally by the reference nu'meralflfi, is shown mounted on the underside of the burner casing H3, Figs. 1 and 2. The space in which this switch may be accommodated is extremely limited, necessitating a very compact switch construction. The switch is required to bevery durable, particularly as regards its ability to .Withstand extreme heat and intermittent cooling. If more than one control switch of this character is employed in the heater control system, it is desirable that as many of the switch parts as possible be standardized so that they may be used interchangeably.

The switch it illustrated in Figs. 2, 3 and 4 satisfies the foregoing requirements and is of simple, economical construction. An important feature of this switch is the one-piece ceramic base i8 (shown in Fig. which in the illustrated embodiment is H -shaped, although in some instances it may be preferred to make it .U- shaped. The flat, parallel leg portions 20 and the transverse portion or crosspiece 22 of the base I8 define rectangular spaces forreceiving a stack of aligned leaf members, including a bimetallic leaf member 24 and resilient contact members 25 to 29.

Referring to Fig. 2, the bimetallic member 24 and the contact members 25, 26 and 2.1 are disposed on the upper side of the transverse part 22 of the base It, while the contact members 28 and 29 are disposed on the underside of the transverse part 22. All of the various leaf. members just mentioned are located between the legs 20 of the base I 8, as stated above. Small insulating sheets 30 and metallic spacers 32 of rectangular configuration are interspersed between the various leaf members in the stack. The entire stack is secured to the transverse part 22 by the threaded end portion 34 of a heat-conducting rod 36, Figs. 2 and 4. This threaded part 34 extends downwardly through the stack and through an aperture in the transverse part 22 and emerges from the bottom side of the stack. An integral shoulder portion 38 of the rod 36 engages the upper side of the stack. Near the lower end of the threaded portion 34 there is a rectangular nut 40, Figs. 2 and 3, which fits between the legs 23 of the ba e l8 and is threaded onto the part 34 to hold the switch stack in place.

Preferably, a shield can 42 of rectangular configuration encloses the extending parts of the various leaf members 24 to 29 and fits over the ceramic base IS, the can 42 being appropriately pressed between the shoulder 38 and the nut 40.

Thus, the switch It is assembled in a very convenient manner.

The contact members 25 to 29 are insulated from each other by the insulating spacers 30, and they are insulated from the threaded part 34 by an insulating sleeve 44 on this part. The contact members may be stacked in any desired fashion on the base l8. Where a large number of contacts'is employed, an H-shaped base as I8 is found most convenient to use. For a smaller number of contacts, a U-shaped base may serve satisfactorily. The parts of the contact members 25 to 29 which'protrude rearwardly from the stack beyond the mouth of the shield can 42 are provided with soldering lugs 46, as shown. If desired, however, the soldering lugs 46 may be disposed on separate pieces mounted adjacent to the respective contact members. The lugs are staggered for convenience in soldering.

One or more spacers 48 may be interposed between the shoulder 38 of the rod 35 and the bimetallic leaf member 24. These spacers 48 afford a heat-conducting path from the shoulder 38 to the bimetallic member 24, so that the member 254 is approximatel at the same temperature as the heat-conducting rod as of the switch. The rod 36 is adapted to extend through a mounting nipple 50, Fig. 2, on the burner casing Ill. The rod 36 has an integral collar 52, adjoining the shoulder portion 38 thereon, and a mounting nut 54 is disposed on the shoulder portion 38. The nut 54 has an internally threaded sleeve which extends beyond the collar 52 and screws onto the nipple 5B for mountin the switch I t on the burner casing ill. The major portion of the rod 38 extends into the interior of the casing H).

The illustrated burner has a metallic vaporizer block 56 disposed within the casing It). On the front platev 52 of this vaporizer block 55 there is mounted a baffle 60 which serves as a combustion chamber for the pilot burner of the heater. The pilot flame emerges through openings such as 32, Fig. 2; in the baffie 60 and is directed toward openings 64 in a pair of burner tubes 66 which serve as combustion chambers for the main burners of the heater. The main burner nozzles 68 extend from the front plate 52 through the openings 64 tangentially into the interior of the burner tube 65. Liquid fuel vaporized within the vaporizer block 56 is mixed with air therein to form combustible fuel and air mixtures which are fed to the pilot burner and the main burners. As the main burner fuel mixtures issue from the nozzles 68 into the tubes 66, they are ignited by the parts of the pilot flame that proiect through the openings 64. The combustion products then pass into the heat exchanger ducts as l2, Fig. 1, that are respectively aligned with the burner tubes 56.

The heat-conducting rod .36 of the switch It extends upwardly adjacent the baffle all so that portions of the pilot flame issuing from the openings 62 can play upon the rod 36. As shown in Fig. 6, the rod 36 has a core 1!] of highly heat-conductive material, such as copper, and this core is surrounded by a sheath or jacket 52 of corrosion-resistant material which will withstand the heat of the pilot flame without deteriorating. -As the rod;36 heats (or cools), the temperature .of the bimetallic member v-24 in theswitch it likewise changes. This causes the contact members 25 to 29 to be actuated for automatically controlling-certain functions of the heater operating system.

Fig. '7 illustrates the portion of theheater operating system which is controlled by the switch [6. -When the heater is in a cold condition initially, and themain switch is turned on, a circuit is closed from :a .l2-volt alternating-current source through the switch contacts 28 and V2!! to an ignitenrepresented by-the coil (4. In "the illustrated heaterthis igniter is of the fuel-burning. type,-and itprovidesan igniter flame that is projected through the openings -62 in thepilot burner bafile 60. As the igniter-flameplays upon the rod 36, heat is transferred through the rod 36 to the bimetallic member 24, causing the latter to flex. Bimetallic member 24, as it flexes, causes the .-contact member 25- to engage the contact member 26, thereby closing .a circuit from a 6- Volt direct-current source to asolenoid 16 which .operates a valve for admittingfuel to the pilot burner of the heater. A pilot flame is established as this fuel is ignited by the flame fromthe igniter. The bimetallic member24 continues to flex and bends the contactmember 2-5 to the right, as viewed in Fig. '7. The contact member 29 carries an insulating stud 1.8 which-bears against the contactimember 25. Therefore, as the bimetallic member bends the member. 28, the contact member 29 also bends and becomes separated from the contact member 28. This interrupts the circuitto the ignitenwhich no longer is required to operate ,oncethepilot flamesis established.

The continued heating of therod .35 and the consequent flexing of the bimetallic memberld causes the contact member. 26 to engage the contact member 21, thus preparing a circuit from the 6-vo lt direct-current source to the movable contactor 80 of a temperature-control switch 82, schematically represented in Fig. 7. The-contactor 80 is actuated by a suitable temperature responsive device, suchas a bellows (not shown) filled with a fluid having a high temperature coeflicient of expansion. This device is located .at any suitable point where it is exposed to the :air that is being heated b theheater. If only a minimum heat is demanded, the contactor 80-remains disengaged from both of 'the .stationary contacts 83 and 84. If the heat demand is moderate, the contactflil engages the contact -83, closing a circuit to ,a solenoid 86 which operates a valve for admitting fuel to one-of the main burners. If the heat demand is heavy, the contactor 80 advances until it engages both of the contacts 83 and 84, thus closing. circuits to the solenoid, 86 and another solenoids}; that ,controls i-a valve for admitting fuel to the other main burner.

If combustion shouldfail within the heater, the flame rod 36 cools. The bimetallicmember 24 thereupon cools also and resumes its normal position as shown in Fig. '7, successively opening the circuits to the main burner solenoids .86 and 88 and the pilot burner solenoid l6, and reestablishing the energizing circuit for the igniter-M. The above described cycle of operations thenis repeated to bring the heater back into operation.

Hence, it will be seen that the thermal control switch I 6 plays a vital part in theautomatic operation ofthe heater. It is. requiredito be deanda-hie .ove l nep riods ;9 -..erYic.e, and .yet

number of different ways.

its cost must :bekeptisufllcientlyilow (particularly .inza small heater) so .that iit isznotva :substantial part of .the-totalcost. The :disclosedswitch: ['6

is simple, cheap and-ruggedhas only a few parts and is of verysmall size. The form of the base l8 permits the contact pile to be arranged in a Thus; the same form of base may be vused for different switches than are associated with the burner structure. Other advantages ofiithe' invention not specifically mentioned above .maywreadily occur to 'those skilled in the art.

While there has been disclosed what is at present considered to be a preferred embodiment of the invention, it willbe understood that various modifications thereof may be made within the truespirit and scope of the invention as defined in the appended claims.

I claim:

1. 'An electric switch of the thermal type comprisingza one-piece ceramic base having two parallel leg portions and'a transverse portion extending between said leg portions, a stack "of aligned .leaf :members having portions thereof disposed: between the leg portions of said base, at least oneof ,said leaf members being abimetallic heat-responsive member, and the other leaf members being resilient contact members arranged -for actuation by said heat-responsive member as the temperature'thereof varies, insulating members interspersed with the contact members in said stack, a heat-conducting rod extending through said stackandsaid'transverse portionpf said base, said bimetallic member being in heat-conductive relationship to said rod and moving in-resp'onse to the heat derived therefrom, said rod having .a shoulder portion'disposed on oneside of said stack" and a threaded end portion protruding from theother side of said stack, and anut threaded on said end portion for securing said stack to said transverse .portion, with the leg portions of said base preventing said leaf members from turning relative to said-rod.

2. An electric-switch of the thermal type comprising a one-piece ceramic base having two flat parallel leg portions and a flat transverse portion extending between said leg portions, a stack of aligned leaf members having portions thereof disposedabetween the leg portions of said base. at least. one of said leafmembers being a bimetallic heat-responsive member and the other leaf members being resilient contact members arranged for actuation by said heat-responsive member as thetemperature thereof varies-an elongated connecting membenexten'ding through said stack and through said transverse :portion for securing saidstack to said base, said'connecting member being of heat-conducting material and being in heat-conductive relation to said bimetallic member to supply heat thereto for causing movement of said bimetallic member, and means in said stack electrically insulating said contact membersfrom said-connecting member and from each other.

.3. An electric switch of the thermal-type comprisinga one-piece ceramic base having two flat parallel legportions and a flat transverse portion extending between said leg portions, a stack of aligned leaf members having portions thereof disposed between the leg portions of 'saidbase, at least one of said leaf members .being'a bimetallic-heat-res-ponsive member, and the other leaf members being individualcontact members-arbitrarily: arranged for actuation bysaid' bimetallic memberas thetemperature thereofvariesbpacers interspersed with said contact members in said members from turning relative to said rod.

4. An electric switch of the thermal type comprising an H-shaped ceramic base having two parallel leg portions and a transverse portion extending between said leg portions, a stack of aligned leaf members having portions thereof disposed between the leg portions of said base on both sides of said transverse portion thereof, at

least one of said leaf members being a bimetallic heat-responsive member and the other leaf members being resilient contact members arranged for actuation by said heat-responsive member as the temperature thereof varies, an elongated connecting member extending through said stack in said transverse portion for securing said stack to said base, said connecting member being of heatconduc-tive material and being in heat-conductive relation to said bimetallic member to supply heat thereto for causing movement of said bimetallic member, and means in said stack electrically insulating said contact members from said connecting member and from each other.

5. An electric switch of the thermal type comprising an H-shaped ceramic base having two flat parallel leg portions and a flat transverse portion extending between said leg portions, a stack of aligned leaf members having portions thereof disposed between the leg portions of said base on both sides of said transverse portion thereof, at least one of said leaf members being a bimetallic heat-responsive member and the other leaf members being resilient contact members arranged for actuation by said bimetallic member as the temperature thereof varies, an elongated connecting member having a portion extending through said stack and said transverse portion for securing said stack to said base, said connecting member being of heat-conductive material and having an extending portion adapted to be positioned in heat-conductive relation to a heat source to transfer heat therefrom to said bimetallic member, and means in said stack electric-ally insulating said contact members from said connecting member and from each other.

6. An electric switch of the thermal type comprising a one-piece ceramic base having two fiat parallel leg portions and a flat transverse portion extending between said leg portions, a stack of aligned leaf members having portions thereof disposed between the leg portions of said base, at least one of said leaf members being a bimetallic heat-responsive member and the other leaf members being resilient contact members arranged for actuation by said heat-responsive member, a heat-conducting rod having a shoulder portion disposed on one side of said stack and a threaded portion extending from said shoulder portion through said stack to the other side thereof, heat transfer means connecting said rod to said heat responsive member for transferring heat thereto for moving said heat responsive member to change the position of said contact members, a shield can enclosing said leaf members and fitted 8 on the exterior of said base, and screw-threaded means'on the threaded portion of said rod for securing said stack and said can to said base.

7. A thermally operated electric switch responsive to the temperature within a casing having an operating portion positioned remote from the casing and a heat conducting portion extending into the casing, said switch including in combination a heat-conducting rod extending into said casing, a ceramic switch base having two parallel leg portions and a transverse portion extending between said leg portions, said transverse portion being aligned with said rod, a stack of aligned leaf members having portions thereof disposed between the leg portions of said base, at least one of said leaf members being a bimetallic heatresponsive member and the other leaf members being switch contact members arranged for actuation by said heat-responsive member, said rod having a reduced portion thereof extending through said stack and through said transverse portion, screw-threaded means on said rod for securing said stack to said base, and heat transfer means connecting said rod to said heat-responsive member so that said heat-responsive member moves to change the position of said contact members as the temperature in said casing varies.

8. A thermally operated electric switch responsive to the temperature within a casing having an operating portion positioned outside the casing and a heat conducting portion extending in the casing, said switch including in combination a heat conducting rod extending into said casing from the exterior thereof, means securing said rod to said casing, and switch means mounted on said rod including a one-piece ceramic base having a pair of flat parallel leg portions and a flat transverse portion extending between said leg portions, said transverse portion being aligned with said rod, a stack of aligned leaf members having portions thereof disposed between the leg portions of said base, said rod having a shoulder disposed on one side of said stack and a threaded portion extending through said stack and through the transverse portion of said base to the other side of said stack, and a nut on said threaded portion of said rod securing said stack and said base thereto, said stack including a bimetallic heat-responsive member in heat-conducting relation to said rod, and a plurality of switch contact members arranged for actuation by said bimetallic member as the temperature of said rod varies in accordance with the temperature within said casing.

9. A demountable thermal electric switch assembly adapted to be removably mounted as a unit on a liquid fuel burner adjacent the combustion portion of the latter in heat conducting relation therewith and adapted to operate in response to temperature changes in such combustion portion, said thermal electric switch assembly including in combination, a plurality of electric contact members having a mounting portion at one end of each and having contact means at the other end through which to make and break an electrical circuit, a heat responsive thermal member for actuating said contact members and having a mounting portion, a stud having a transverse shoulder portion and having said contact members and said thermal member mounted thereon at the mounting portions of said members with said members extending transversely of the direction of said stud, electrical insulating means separating each of said contact members and said thermal member from one another at 10 parallel with the wall of the combustion portion so as to be compactly associated with said wall.

MICHAEL J. LAROCCO.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,260,647 Vanatta Oct. 28, 194.1 10 2,286,857 Holthouse June 16, 1942 2,317,033 Dafiorn Apr. 20, 1943 2,394,121 Ulanet Feb. 5, 19%6 

